As produced, e.g., by a fluid bed reactor, such as the reactors shown in U.S. Pat. Nos. 4,868,013; 5,139,762; and 8,075,692, granular polysilicon typically contains from 0.25% to 3% powder or dust by weight. The powder may render the product unsuitable for certain applications. For example, a product containing such levels of powder typically is unsuitable for use in producing monocrystalline silicon since the powder can cause a loss of structure, making single crystal growth impossible.
Current wet processes for removing dust have some disadvantages because there is complex, costly equipment to maintain, water and/or chemicals are required, and the processing may cause excessive oxidation of the polysilicon. Dry processes may avoid these disadvantages, but in at least some cases, the amount of powder or dust in the product may not be reduced to acceptable levels for monocrystalline silicon applications. Thus there is a demand for additional methods for producing granular polysilicon with reduced dust or powder levels.